Neuroectodermal fate of epiblast cells in the distal region of the mouse egg cylinder: implication for body plan organization during early embryogenesis

Abstract

The developmental fate of cells in the distal region (distal cap) of the epiblast was analysed by fate mapping studies. The displacement and differentiation of cells labelled in situ with carbocyanine dyes and lacZ-expressing cells grafted to the distal cap were studied over a 48-hour period of in vitro development. The distal cap epiblast differentiates predominantly into neurectodermal cells. Cells at the anterior site of the distal cap colonise the fore-, mid- and hindbrain and contribute to non-neural ectoderm cells of the amnion and craniofacial surface ectoderm. Those cells in the most distal region of the epiblast contribute to all three brain compartments as well as the spinal cord and the posterior neuropore. Cells at the posterior site of the distal cap are mainly localised to the caudal parts of the neural tube. A minor contribution to the embryonic (paraxial and lateral) and extraembryonic (allantoic and yolk sac) mesoderm is also found. Epiblast cells located outside the distal cap give rise to surface ectoderm and other non-ectodermal derivatives, with only a minor contribution to the neuroectoderm. Results of this study provide compelling evidence that the precursor population of the neural tube is contained in the distal cap epiblast of the early-primitive-streak-stage embryo. Furthermore, the regionalisation of cell fate within this small population suggest that a preliminary craniocaudal patterning may have occurred in the neural primordium before neurulation.